It’s March, and the sap is soon to rise, igniting spring fever in us all. But in one respect I’m sorry to see winter go. It is the sweet season, when hunkered-down vegetables, their growth suspended, hoard their sugars. For those who garden in winter, such knowledge is the lore of a secret society, hidden in the earth.

On a recent mid-February visit to Southern Maryland, my husband and I spent an afternoon nibbling our way through the fields of Even’ Star Farm near the shores of Chesapeake Bay. Traces of snow sprinkled the ground as we strolled, bundled in coats, unwarmed by the weak sun. The farmer, Brett Grohsgal, guided us across the flat, well-managed fields, picking bits of roots and leaves for us to try.

A cylindrical, pink-shouldered turnip called Colletto Viola had crisp white flesh within, astonishingly juicy and mild. Planted in late September, it shared space with a soil-improving crop of vetch. Grohsgal unearthed a White Egg turnip and another called Gold Ball that buries itself protectively in the soil. Both were sweet and delicious, thanks to the frosty ground.

This was familiar territory for us, since we too are winter growers, but as we moved on to Grohsgal’s cold-hardy greens, we were excited by the complexity of their flavors. Next to a windbreak fence covered with Triple Crown blackberry vines, we discovered his Even’ Star Smooth Kale, unusually tender and sweet. So was his Tender Tat, a cross between tatsoi and an Asian mustard called Tendergreen, more upright than the standard mat-like tatsoi. Our favorite was his Chinese Thick-Stem Mustard. Nibbling on the small, gritty leaves, we felt waves of sweetness and heat, as if a dozen different flavonoids were zinging around in our mouths. “In a greenhouse there would only be six,” Grohsgal said matter-of-factly. “It’s the cold that does it.”

It’s also the breeding. Our guide spent much of his life as a chef and is first and foremost a seeker of flavor. This passion led him to his current work of developing hardier, tastier varieties of winter vegetables, especially brassicas (we also saw arugula, rapini and numerous other winter stalwarts). Choosing to grow them outdoors, unprotected, in a climate where what he does is just barely possible, has allowed him to select the year’s hardiest, best-tasting plants, harvest only some of their leaves and then let them go to seed.

When sown, these seeds impart those traits to the next generation, so that each year the variety is improved. As a result, Grohsgal has become not only a market gardener but also a breeder of note, with many of his selections listed for sale in both the Southern Exposure (www.southernexposure.com) and Fedco (www.fedcoseeds.com) catalogues.

Go out and look at your garden. Is there anything green left in it? If you find a cabbage, a radish, a mustard, a turnip, take a nibble quick. Before it’s spring.

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